Microcrystalline cellulose, also known as MCC or cellulose gel, is commonly used in the food industry to enhance the properties or attributes of a final food product. For example, it has been used as a binder and stabilizer in food applications, including in beverages, and as stabilizers. It has also been used as a binder and disintegrant in pharmaceutical tablets, as a suspending agent in liquid pharmaceutical formulations, and as binders, disintegrants, and processing aids in industrial applications, in household products such as detergent and/or bleach tablets, in agricultural formulations, and in personal care products such as dentifrices and cosmetics.
Microcrystalline cellulose is produced by treating a source of cellulose, preferably alpha cellulose in the form of pulp from fibrous plant materials, with a mineral acid, preferably hydrochloric acid (acid hydrolysis). The acid selectively attacks the less ordered regions of the cellulose polymer chain thereby exposing and freeing the crystalline sites which form crystallite aggregates which constitute the microcrystalline cellulose. These are then separated from the reaction mixture, and washed to remove degraded by-products. The resulting wet mass, generally containing 40 to 60 percent moisture, is referred to in the art by several names, including ‘hydrolyzed cellulose’, ‘hydrolyzed cellulose wetcake’, ‘level-off DP cellulose’, ‘microcrystalline cellulose wetcake’, or simply ‘wetcake’.
The classic process for MCC production is acid hydrolysis of purified cellulose, pioneered by O. A. Battista (U.S. Pat. Nos. 2,978,446; 3,023,104; and 3,146,168). In efforts to reduce the cost while maintaining or improving the quality of MCC, various alternative processes have been proposed. Among these are steam explosion (U.S. Pat. No. 5,769,934; Ha et al.), reactive extrusion (U.S. Pat. No. 6,228,213; Hanna et al.), one-step hydrolysis and bleaching (World Patent Publication WO 01/0244; Schaible et al.), and partial hydrolysis of a semi-crystalline cellulose and water reaction liquor in a reactor pressurized with oxygen and/or carbon dioxide gas and operating at 100 to 200° C. (U.S. Pat. No. 5,543,511; Bergfeld et al.).
Microcrystalline cellulose and/or hydrolyzed cellulose wetcake has been modified for a variety of uses. In food products it is used as a gelling agent, a thickener a fat substitute and/or non-caloric filler, and as a suspension stabilizer and/or texturizer. It has also been used as an emulsion stabilizer and suspending agent in pharmaceutical and cosmetic lotions and creams. Modification for such uses is carried out by subjecting micro-crystalline cellulose or wetcake to intense attrition (high shear) forces as a result of which the crystallites are substantially subdivided to produce finely divided particles. However, as particle size is diminished, the individual particles tend to agglomerate or hornify upon drying. A protective colloid (such as sodium carboxy-methylcellulose (CMC)) may be added during attrition or following attrition but before drying. The protective colloid wholly or partially neutralizes the hydrogen or other bonding forces between the smaller sized particles. Colloidal microcrystalline cellulose, such as the carboxymethyl cellulose-coated microcrystalline cellulose described in U.S. Pat. No. 3,539,365 (Durand et al.). This additive also facilitates re-dispersion of the material following drying. The resulting material is frequently referred to as attrited microcrystalline cellulose or colloidal microcrystalline cellulose.
On being dispersed in water, colloidal microcrystalline cellulose forms white, opaque, thixotropic gels with microcrystalline cellulose particles less than 1 micron in size. FMC Corporation (Philadelphia, Pa., USA) manufactures and sells various grades of this product which comprise co-processed microcrystalline cellulose and sodium carboxymethylcellulose under the designations of, among others, AVICEL® and GELSTAR®.
There remains a need, however, for a method of making a colloidal microcrystalline cellulose:carboxymethyl cellulose composition with enhanced stabilization, improved gel strength G′, and other desirable rheological properties useful in a variety of applications, and particularly in food products.